Allergic disorders of the ocular surface include a wide variety of pathological conditions including Seasonal Allergic Conjunctivitis (“SAC”), Perennial Allergic Conjunctivitis (“PAC”), Vernal Keratoconjunctivitis and Atopic Keratoconjunctivitis. It is estimated that over 20% of the general population suffer from some form of ocular allergy. Of those, approximately 90% suffer from either SAC, PAC or both.
The ocular allergic reaction is an IgE-dependent (Type I) hypersensitivity inflammatory response that most commonly affects adults between 20 and 40 years of age. In susceptible individuals, initial exposure of allergen to the ocular surface stimulates the production of allergen specific immunologic antibodies (IgE). IgE then binds to the membrane bound Fc.epsilon.R-1 receptor of naive mast cells in the ocular mucosa. The mast cell is a granulocyte, containing a number of preformed mediators, including histamine and proteoglycans. Once the mast cell is activated, newly formed chemical mediators are formed, which include prostaglandin D2, leukotrienes, and platelet aggregating factor. Subsequent exposure of allergen to the IgE coated mast cells leads to the release of preformed, as well as newly formed, mediators contained within the granules of the mast cell.
The clinical symptoms of allergic conjunctivitis include itching, redness, swelling of the eyelid, chemosis and tearing. Histamine is the primary mediator in the allergic response. After mast cell degranulation, histamine binds to receptors located in the conjunctiva. The binding of histamine to H1 receptors on nerve cells induces itching. Activation of H1 and H2 receptors on the vaso-endothelium induces vasodilatation and increases vascular permeability facilitating the migration of inflammatory mediators, such as IL-1α and IL-1β, into the blood vessel and the subsequent recruitment of leukocytes into the conjunctival tissue. Activation of the histamine receptors leads to ocular hyperemia, chemosis, lid swelling and exudation of fluid from blood vessels into the surrounding tissue, which in turn causes inflammation. The chemotaxis of leukocytes such as eosinophils and neutrophils into the conjunctival tissue in turn leads to further tissue damage.
Historically, antihistamines have been the mainstay for treatment of ocular allergic disease. These therapies vary in potency, specificity and duration of action. First generation anti-histamines such as pheniramine and antazoline are known for their rapid onset of action. Unfortunately, these compounds also cause ocular discomfort and their efficacy diminishes after only a few hours. Second-generation H1 antagonists such as levocabastine and emadastine present less ocular discomfort and have a somewhat longer duration of action. However, these compounds have limited anti-inflammatory effects, and do little to inhibit the late-phase components of the inflammatory response.
Currently, the most effective therapies for the management of ocular allergy are drugs such as olopatadine, ketotifen and azelastine, which have both anti-histaminic and mast cell stabilizing properties. These therapies are generally well tolerated and their effects can last up to 8 to 12 hours. Although reported to be superior to compounds that effect only a single component of the allergic response, these compounds often fail to provide relief more than one ocular allergy symptoms.
A drug's affect on ocular redness, chemosis and eyelid swelling offers a significant improvement over existing therapies. Additionally, since the majority of newer ophthalmic anti-allergic agents have limited durations of action, twice daily dosing is required. A topical preparation with a longer duration of action will be advantageous because it may be instilled once daily. Thus, new therapies that can offer advantages in areas such as efficacy and duration of action, while offering similar safety profiles, are needed. The instant invention is directed to these and other objectives.